1. Field of the Invention
This invention lies in the field of hoisting equipment. More particularly it relates to the design of a hoisting system that can be converted quickly from a four line travelling block, to a two line travelling block without having to detach and rethread the cable through the blocks.
2. Description of the Prior Art
In the prior art there are hoisting systems that require a four line travelling block because of the lifting requirements, while at other times, they could use a two line travelling block because the lifting requirements were reduced, but the speed requirements were increased. In order to do this, it was generally necessary to detach the dead line and restring the cable out of the four line block into a two line block, and so on, and then to reattach the dead line to the boom. This requires a considerable amount of time and difficulty and which limited its use, whereas a simpler system, such as the present invention, might well have been put to use on many occasions.